Why doesn't chrome cache google app engine blobstore - google-app-engine

Question

I'm using blobstore to serve audio files embedded in HTML5 audio element. Because I have a blobkey as a part of url I can assume that for any given url its content will never change. That looks like a perfect setup for caching.
Yesterday I implemented a solution which seemed to work. At least I remember that it worked ;). Unfortunately today I discovered, that it doesn't work with Chrome and production server. It works perfectly with Internet Explorer and Firefox. It even works with Chrome and development server - I use version 1.7.6. My solution uses Cache-Control headers, but it seems that only Firefox makes any use of it. Additionally I added an ETag header. When I discover If-None-Match request header with the same value I return 304 code. That seems to work with Internet Explorer. It also works with Chrome and development server. I remember that it had worked yesterday with Chrome and production, but I'm not completely sure. Anyway the problem I have is why both caching mechanisms are ignored by Chrome. I suspect that it may have something to do with chunked encoding which is generated only for chrome, but I don't understand why caching is disabled in that case
And now a lot of details.
Firefox
Initial request headers:
Host: eduzabawy.appspot.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:20.0) Gecko/20100101 Firefox/20.0
Accept: audio/webm,audio/ogg,audio/wav,audio/*;q=0.9,application/ogg;q=0.7,video/*;q=0.6,*/*;q=0.5
Accept-Language: pl,en-us;q=0.7,en;q=0.3
Range: bytes=0-
Referer: http://eduzabawy.appspot.com/dziecko/
Cookie: children="jEDor1B8VRDRJreWmUVlUQ\075\075"; session=eyJfc2lkIjoiWk91QmlsOEJlTEd4QVFuYVFiYkpsTyJ9|1365190508|81d81772f6f409dd57ad43a9f447f92d1b56d29e
Connection: keep-alive
Initial response headers:
HTTP/1.1 206 Partial Content
Cache-Control: public max-age=100000000
Content-Range: bytes 0-37249/37250
Content-Type: audio/ogg
Date: Fri, 05 Apr 2013 19:45:47 GMT
Etag: blobstore
Server: Google Frontend
X-Firefox-Spdy: 3
On subsequent loads it seems that Firefox doesn't even try to fetch the files. This is how I thought it should work.
Internet Explorer
Initial request headers:
Accept: */*
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
Referer: http://eduzabawy.appspot.com/dziecko/
Accept-Language: pl-PL
Accept-Encoding: gzip, deflate
Host: eduzabawy.appspot.com
Connection: Keep-Alive
Cookie: children="WyzUQwHEzwX6qnjfn21KEw\075\075"; session=eyJfc2lkIjoia2VOd0llR0hvRHU1cUN0cE1QSWRpWCJ9|1365192921|f2279f82b21947c4d064dbf44a5ce9e1bd95cc0d
Initial response headers:
HTTP/1.1 200 OK
Cache-Control: public max-age=100000000
ETag: blobstore
Content-Type: audio/mpeg
Date: Fri, 05 Apr 2013 20:15:23 GMT
Server: Google Frontend
Content-Length: 4637
Subsequent request headers:
Accept: */*
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
Referer: http://eduzabawy.appspot.com/dziecko/
Accept-Language: pl-PL
Accept-Encoding: gzip, deflate
Host: eduzabawy.appspot.com
If-None-Match: blobstore
Connection: Keep-Alive
Cookie: children="WyzUQwHEzwX6qnjfn21KEw\075\075"; session=eyJfc2lkIjoia2VOd0llR0hvRHU1cUN0cE1QSWRpWCJ9|1365192921|f2279f82b21947c4d064dbf44a5ce9e1bd95cc0d
Subsequent response headers:
HTTP/1.1 304 Not Modified
ETag: blobstore
Content-Type: audio/mpeg
Content-Length: 4637
Chrome + development server
Initial request headers:
Host: localhost:8080
Connection: keep-alive
Accept-Encoding: identity;q=1, *;q=0
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.43 Safari/537.31
Accept: */*
Referer: http://localhost:8080/dziecko/
Accept-Language: pl-PL,pl;q=0.8,en-US;q=0.6,en;q=0.4
Accept-Charset: ISO-8859-2,utf-8;q=0.7,*;q=0.3
Cookie: children="xYNsqzfdtZ-2Z764lFSzk1Ed8-g1QoNlcaexsD79gSY\075"; session=eyJfc2lkIjoiTE9CZDc0SHJENHF4OWJua1J4S3dTQSJ9|1365192253|37815772acab0bf44a0c501ea0fd0dc7c617dd09
Range: bytes=0-
Initial response headers:
HTTP/1.1 206 Partial Content
etag: blobstore
cache-control: public max-age=100000000
content-type: audio/mpeg
Content-Range: bytes 0-4636/4637
Content-Length: 4637
Server: Development/2.0
Date: Fri, 05 Apr 2013 20:32:19 GMT
Subsequent request headers:
Host: localhost:8080
Connection: keep-alive
Accept-Encoding: identity;q=1, *;q=0
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.43 Safari/537.31
Accept: */*
Referer: http://localhost:8080/dziecko/
Accept-Language: pl-PL,pl;q=0.8,en-US;q=0.6,en;q=0.4
Accept-Charset: ISO-8859-2,utf-8;q=0.7,*;q=0.3
Cookie: children="xYNsqzfdtZ-2Z764lFSzk1Ed8-g1QoNlcaexsD79gSY\075"; session=eyJfc2lkIjoiTE9CZDc0SHJENHF4OWJua1J4S3dTQSJ9|1365192253|37815772acab0bf44a0c501ea0fd0dc7c617dd09
Range: bytes=0-4636
If-None-Match: blobstore
Subsequent response headers:
HTTP/1.1 304 Not Modified
Content-Type: text/html
Server: Development/2.0
Date: Fri, 05 Apr 2013 20:33:08 GMT
Chrome + production server
Initial request headers:
Host: eduzabawy.appspot.com
Connection: keep-alive
Accept-Encoding: identity;q=1, *;q=0
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.43 Safari/537.31
Accept: */*
Referer: http://eduzabawy.appspot.com/dziecko/
Accept-Language: pl-PL,pl;q=0.8,en-US;q=0.6,en;q=0.4
Accept-Charset: ISO-8859-2,utf-8;q=0.7,*;q=0.3
Cookie: children="sU9aqnqEf67eZFpS7BKSMw\075\075"; session=eyJfc2lkIjoieFlGWlJLMnRwSHJuOVFCb1haTnJLUCJ9|1365194193|2a13cd9eb7aceeb40c43bd82a763d893436d9f1f
Range: bytes=0-
Initial response headers:
HTTP/1.1 206 Partial Content
Cache-Control: public max-age=100000000
ETag: blobstore
Content-Type: audio/mpeg
Content-Range: bytes 0-4636/4637
Date: Fri, 05 Apr 2013 20:36:35 GMT
Server: Google Frontend
Transfer-Encoding: chunked
Subsequent requests and responses are the same as initial.

Answer 1

Your max-age seems too long and going over 3 years... I read from somewhere the maximum you should set in GAE is no more than 1 year.
Anyway, there's one more header you should try to set (Pragma: Public), which worked for me (I'm caching image from blobstore though, here's a few lines from my source code):
httpResponse.Header().Set("Cache-Control", "public, max-age=600")
httpResponse.Header().Set("Pragma", "Public")
blobstore.Send(httpResponse, project.ImageBlobKey)
By the way the above also cause Google to delivery your file from the edge cache, which really speed static resources up a lot!